Method and means for controlling tube characteristics



c. w. HANSELL A 2,080,204'

METHOD AND MEANS FOR CONTROLLING TUBE CHARACTERISTICS Filed Dec. 12, 1925 2 Sheets-Sheetl M I I I I j INVENTOR cumeuce w. HANSELLI TORNEY y 1937- I c. w. HANSELL 2,080,204 1 METHOD AND MEANS FOR CONTROLLING TUBE CHARACTERISTICS- Filed Dec. 12, 1925 2 Sheets-Sheet 2 HlllLllllll:

INVENTOR CLARENCE w. HANSELL ATTORNEY FFEQ NlTED s'rA'res METHOD AND MEANS FOR GONTROLLING TUBE CHARACTERISTICS Clarence W. Hansell, Rocky Point, N. T1, assignor to Etadio Corporation of America, a corporation of Delaware Application December 12, 1925, Serial No. 74,938

29 Claims. (01. 179- 171) This invention relates to the use of amplifiers, However, if the ratio of output to input does not oscillators, detectors, modulators and any other remain constant at the correct value the two rectype of device using vacuum tubes in which it tified currents will become unequal and there will is desirable that the input bear a definite relabe a resultant current and voltage drop in the 5 tion to the output. Particularly, the invention common resistance. This voltage drop is utilized relates to the control of the ratio of the input to vary the grid potential, and therefore the amto the output so that a true reproduction of the plification, of one or more stages of the ampliinput will result according to the design for which fier system in such a way as to correct the ratio the apparatus was built. The embodiment hereof output to input.

in disclosed is an amplifier, and while the ex- The time constant of the rectifier circuits, of 10 planation following will be limited to the use of course, is such that the time required for the amplifiers, requiring a linear characteristic, it is correction to take place is small compared with not intended that the principles stated be so the modulating frequency of the currents to be limited. amplified.

l5 The causes of the non-linear characteristic of As an alternative to the method which has been amplifiers such as can now be built, are:- described it is possible to correct the dropping 1. At a certain amplitude of input and output of the amplitude characteristic of an amplifier the vacuum tubes begin to draw grid current and due to grid rectification only. In. this method the the regulation. of the grid excitation circuits torectified direct current of one stage of amplifier 2O gether with regulation within the tubes, due to a is used to change the bias and amplification of 2C portion of the emission being taken by the grid, another stage in such a manner as to correct the cause a departure from the normal amplitude characteristic. characteristic. In both the methods which have been described 2. Even if the tubes could be designed to operit is very desirable to use the push-pull ampliate over the whole range of their direct current fier circuit so that rapid corrections of the bias 25 output without grid current their characteristics potential an amplifier will not set up surges introduce some departure from a linear characin the amplifier output which could cause asteristic. cillations or damage to the system. However,

The first cause can be relieved to some extent by other types of amplifiers, modulators, or osmodifications in the design of the tubes or by cillators might be used in the same way. running with low output from the tubes. There Further and more specific advantages will be has been no apparent wayfor eliminating distorobserved in connection with the annexed detailed tion due to the second cause. description, claims and drawings in which:--

A method for eliminating, or very greatly re- Fig. 1 shows one arrangement for producing ducing the departure from a non-linear characthese results in a multi-stage amplifier, and 35 teristic, due to any cause, is shown schematically Fig. 2 shows a slightly different method, in the drawings hereto annexed. I shows the input terminals to the input trans- The scheme consists of a method for automatiformer 2 coupled to the grids of tubes 4 and 5. cally causing the amplification of one or more The middle point of the transformer secondary 40 stages of an amplifier system to be varied by varyis connected to the bias battery 3 which gives a 4 ing the grid bias to keep a constant ratio between constant bias to the grids. The plates of these the input and output amplitudes of the amplifier tubes are energized by the high potential battery system. 3! through the connection 8 of the output trans- This is accomplished by coupling two rectifier former I,

circuits respectively to the input and output cir- The oscillations thus produced pass through 4: cuits and applying their rectified currents differthe transformer 9 to the second stage amplifyentially to a resistance or reactance common. to ing tubes II and I2. The filaments of these tubes both rectifier circuits. The rectified current are connected as in the first stage to the negathrough the common resistance or reactance protive terminal of the high potential battery and duced by each rectifier is proportional to the alalso to another conductor at [4; The grids of 51 ternating current voltage of the coupling in the these tubes are connected to another bias batcircuit and normally if their is a correct ratio of tery Ill. The plates of these tubes are energized output to input the two rectified currents will be through connection It and oscillations are introequal and produce no voltage drop in the common duced into the transformer i5. This transformer reactance, is connected to transformer ll of the 3rd stage, 5!

having tubes [8 and L9. The grids of these tubes are biased by the battery 20 as in the case of the first stage. The plates are energized through the connection 2| and the output appears in the coil 22,

To the first input transformer 2 or to the input circuit there is variably coupled a third winding 6 and to the output transformer or output circuit there is also variably coupled a third winding 23. These two windings are connected together so as to be approximately in phase with each other through rectifiers 24 and Z5 and the resistances or reactances 26 and 21 variable if desired. Between these is a third resistance or reactance 28 with the by-pass condenser 29 for the radio frequencies. To this same mid-point, a third connection is made at 30 to the other side of the bias battery It]. It can thus be seen that the bias produced by the battery It! on the grids of the tubes 1 l or I2 will be modified by any potential difierence across resistance or reactance 28.

The number of turns on coils 6 and 23 are so selected that with the normal amount of amplification there will be no flow of current through 28. If more current is passed through rectifier 24 than through rectifier 25, a potential dinerence would exist in one direction across 23. If more passes through 25 than 24 a reverse potential difference will exist. Thus, the bias produced by battery Ill will be added to or subtracted from by the amount of the potential difference across 28, and in direct ratio to the amount of power unbalance between the coils 6 and 23.

If the proper couplings are obtained in the input and the output transformers, a constant ratio of power transformation may be obtained in the coils 6 and 23.

In the operation of this arrangement, the output may be slightly decreased for the very small amount of power input but for large or average amounts of power input, a much greater amount of the power output would be obtained due to the automatic grid bias regulation. In this way, any natural characteristic of the amplifier system as a whole resulting from excess load will be obviated to a considerable extent. This will result in a better operation characteristic in the amplifier and make it graphically nearly a straight line.

With reference to Fig. 2, 32 are the input terminals connected to transformer 31 The tubes 36 and 31 of the first stage of amplification have their plates connected through the transformer 39 and are energized by the battery W. The bias of the first stage is obtained on the grids by the source 35 connected to the negative of the battery 41 and to the filament of the tubes in the second stage M, 42. The output of the second stage has a suitable transformer M energized at the connection 43 by the high potential battery 41. The output is taken off at the terminals 45. In the second stage-the grid bias battery 49 is connected to the middle of the secondary transformer 39. The other side of the bias battery 40 is connected to conductor 34 which is directly connected to the filaments of the first stage. Between this conductor and the filaments of the second stage is the resistance, reactance or other impedance G6.

In this arrangement it is obvious that the grid current of tubes 4| and 42, which must be a function of the input power, affects the potential difference between grid and filament of tubes 36 and 31 through its effect upon the potential drop through element 46. This current will produce a voltage drop across 46 which will, in turn, modify the effective bias given to the grids of the first stage by source 35 and the fiow of first stage anode current through element 46. It is possible, with this arrangement, to obtain a straight line operating characteristic throughout the normal range of operation of this arrangement. Proper selection and adjustment of the circuit elements, particularly of impedance 46 will effect this characteristic.

It is not intended to be limited by the construction herein set forth but as indicated before, this arrangement could be used with modulators, oscillators, detectors, etc., and proper equivalents could be substituted for those used at present.

' I wish to be limited only by the scope of the following claims:

1. In combination, several electron emission tube stages, grid bias means, input and output circuits, comparison circuits coupled with said circuits and including rectifying and impedance elementsfand means coupling the bias means and the impedance elements to vary the grid bias according to the ratio of currents in the input and output circuits.

2. In combination, several electron emission tube stages, grid bias means, circuits coupling the input and output circuits including adjustment means, rectifiers for rectifying input and output energy, and means across which rectified current from the rectifiers tends to create a potential gradient, and means to affect the bias means in a manner dependent on the said potential gradient in order to obtain automatic modification of the bias means.

3. In combination, an amplifier having an adjustable ratio of amplification, input and output circuits, means coupling the input and output a desired ratio, for all values of input, and automatically varying the characteristics of the oscillation devices in response to the difference between the actual and desired ratios to reduce the difference.

5. The method of preventing distortion in os-- cillation devices by keeping the ratio of input and output constant for all values of input up to the maximum which includes comparing the actual ratio of input to output with a desired ratio at every instant during the oscillation cycle and controlling the characteristic of the oscillation device during the oscillation cycle to lessen the diiference and obtain the desired ratio.

6. A distortionless amplifier for producing in its output circuit an exact amplified replica of the wave applied to its input circuit comprising several electron emission tube stages, grid bias means, input and output circuits, means associated With said circuits for detecting distortion, and, means for affecting the bias means in response to said distortion detecting means to obviate the distortion whereby the output of said amplifier is substantially an exact amplified replica of the input.

7. The method of obtaining a desired charac- 'teristic from an amplifier employing an'electron emission. tube subjected. to grid. rectification thereby having a. characteristic different from that desired which includes combining. with input energy to a tube fluctuating energy derived from the output energy of the tube suchv that the altered resulting. input energy causes an energy output from the apparatus which is in a desired substantially straight line relation. to the original input energy to the apparatus.

8. The method of obtaining a linear amplificationcharacteristic from an amplifier subject to grid rectification employing an electron emission tube having a non-linear characteristic which includes combining-with the input energy to a tube, relative to the input energy, low frequency fluctuating energy derived from the output and input energies of the tube of such magnitude and phase that the resulting-altered input energy causes an energy output from the amplifier which is in linear relation to the energy input to the amplifier.

, 9. The method of obtaining a desired characterlstic from an electron emission tube stage employing an electron emission tube having a. characteristic different from that desired which includes continuously detecting the magnitude of the departure of the output and the inputof: the stage from the desired characteristic and simultaneously commensurately altering the wave form of input energy applied to a tube grid in response to the detected departures to obtain on the grid an artificial waveof such form that the resulting output wave is in the desired relation to the original input wave.

10. The method of obtaining a linear amplification characteristic from an amplifier employing an electron emission tubehaving a nonlinear characteristic which includes continuously comparing the input to output ratio with that desired and alteringthe Wave form of input energy in response to departure from the desired ratioto obtain an artificial input wave of such form that the resulting output wave is in linear relation to the original input wave.

11. The method of obtaining a linear amplification characteristic from an amplifier subjected to grid detection, employing a plurality of electron emission tubes arranged in cascade and, having non-linear characteristics when the normal grid bias is constant which includes so varying the normal grid bias of one of said tubes, upon variation of input energy to the amplifier, that the resultant output from the amplifier follows a linear characteristic.

12. The method of obtaining a linear amplification characteristic from an amplifier employing an electron emission tube having a, non-linear adjustable characteristic which includes detecting the magnitude of the departure from a linear characteristic during variation of the input to the amplifier and commensurately adjusting the tube characteristic in response to the detected departure to counteract the departure.

13. The method of obtaining a linear amplification characteristic from an amplifier employing an electron emission tube having a non-linear characteristic when the normal potential in one of its associated circuits is constant which includes detecting the magnitude of the departure from a linear characteristic and commensurately varying the normal potential in the associated circuit in response to the detected departure to so change the characteristic that the departure is counteracted.

14. The method of obtaining a linear amplification. characteristic from an. amplifier; employing an electron emission tubehavinga non-linear characteristicwhen the normal grid bias is constant which includes detecting the magnitude of the departure from a linear characteristic and commensurately varying the normal grid bias in response to the detected departure to counteract the departure.

15. The method. of obtaining a linear amplification characteristic from an amplifier employing an electron. emission tube having a nonlinear amplification characteristic which in cludesobtaining. energy which is a function of the input energy, obtaining energy which is a functionfof the output energy, comparing their ratio with. a desired ratio; obtaining corrective energy which is a function of the departure of the actual. ratio from the desired ratio, and using the corrective energy to vary the grid bias of a tube to make the ratioof. input to output of the amplifier: approach. the ratio desired 16. The method of obtaining a linear amplification characteristic from an amplifier employing an. electron emission tube having a non-linear amplification characteristic which includes obtaining and rectifying energy which is a function of the input energy, obtaining and rectifying energy which is a function of the output energy, differentially combining: the rectified energies to obtain a normal resultant when the amplification ratio is that desired, andutilizing changes from the normal resultant to vary the grid bias of a tube to make the amplification ratio of th amplifier-approach that desired. r

17:. The method of controlling. the ratioof am plification. of an amplifier employing an electron emission tube which includes. continuously con paring the input and output energies to ascertain the relation between their ratio and the desired ratio, and continuously utilizing departures of their ratio from the desired ratio to vary a tube characteristic to'lessenthe departure of the actual ratio from. the desired amplification ratio.

18. An electron emission tube amplifier stage reproducing in its output circuit a substantially exact amplified copy of input energy comprising a source of input energy, an input circuit, an output circuit, an electron emission tube subjected to grid rectification thereby having a characteristic other than that desired, and means for applying to the'input circuit of the tube energy derived from the input and output circuits of the tube which combines with and s0 alters the effective wave form of the tube input energy that the output energy is related to the original input energy in accordance with the desired characteristic, reproducing the input energy in substantially exact amplified form.

19. An electron emission tube stage of desired characteristic comprising a source of input energy, an input circuit, an output circuit, an electron emission tube having a characteristic other than that desired, means for difierentiallycombining portions of the input and output energies, and means for combining the differential energy with the input energy to obtain analtered effective input on the tube grid resulting in output energy which is related to the original input energy in accordance with the desired characteristic.

20. An electron emission tube stage of desired characteristic comprising a source of input energy, an. input circuit, an output circuit, an electron. emission. tube having a characteristic other than that desired, auxiliary circuits including rectifying means so coupled to the input and output circuits that the rectified currents are equal when the characteristic is that desired, means for differentially combining the rectified currents, and means responsive to the resultant rectified current for altering the tube characteristic to lessen the resultant current.

21. In combination, an electron emission tube amplifier stage reproducing in its output circuit a substantially faithful amplified copy of the input energy including a tube having a control electrode, an input circuit for feeding energy to the electron emission tube stage, an output circuit for delivering energy from the electron emission tube stage for utilization, and means for automatically adjusting the value of the bias on the aforesaid control electrode comprising an auxiliary detector, means coupling the auxiliary detector to the output circuit of the electron emission tube stage, an impedance arranged to be fed by the output of the auxiliary detector, and means coupling said impedance to the aforesaid control electrode to impress a potential thereupon dependent upon the magnitude of the flow of rectified current through said impedance.-

22. An electron emission tube arrangement for preventing distortion due to grid rectification comprising several electron emission tube stages, grid biasing means therefor, input and output circuits for said stages, circuits, coupled with said input and output circuits, including rectifying and impedance elements, and means for automatically varying the biasing means according to the rectified current flow through said rectifying and impedance elements in order to control in desired fashion the characteristic of the arrangement such that despite grid rectification the ratio of output to input is substantially a straight line.

23. In electrical apparatus of the character described, a pair of electron discharge devices each having an anode, a cathode and a control electrode, said devices being connected in pushpull fashion, an input circuit for said devices, an output circuit for said pushpull connected devices, said devices being subject to grid rectification whereby its characteristic curve is given a form producing distortion in the energy appearing in the output circuit of said pushpull connected electron discharge devices, and means, connected with electrodes of said devices for subjecting automatically and purely electrically said electrodes to more positive potentials when said devices tend to introduce distortion such that the effects of grid rectification are substantially compensated and thereby eliminating substantially the distortion produced by the grid rectification.

24. In electrical apparatus of the character described, an amplifier producing distortion in energy of amplitude beyond a certain value applied to its input circuit, an amplifier preceding said distortion producing amplifier and feeding energy to be amplified to said distortion producing amplifier, and means associated with said amplifiers for increasing the amount of energy fed to the input circuit of said distortion producing amplifier when distortion begins to occur therein, whereby the output of said distortion producing amplifier is substantially an exact reproduction of energy fed to its input circuit despite the inherent distortion characteristic of said amplifier.

25. In electrical apparatus for producing exact but amplified replicas of desired electrical waves, an electron discharge device amplifier element subjected to grid rectification thereby producing,

normally, distortion in the shape of the wave traversing said apparatus, an amplifying electron discharge device preceding said element and feeding Waves thereinto, and a circuit, coupled to said preceding electron discharge device and said amplifier element responsive to the distorting conditions in said element, subjecting said preceding amplifying electron discharge device to potentials such that said preceding device introduces in said amplifiying element correcting potentials compensating and substantially eradicating the distortion normally introduced by said amplifying element.

26. In electrical apparatus, an amplifier having an adjustable ratio of amplification, input and output circuits coupled to said amplifier, a circuit coupled to said input and output circuits automatically controlling and maintaining constant the ratio of output to input energy of said amplifier over a wide range including points where normally grid rectification in said amplifier would occur, and, means for varying the ratio of output to input energy of said amplifier maintained by said automatic ratio controlling circuit.

27. In electrical apparatus, an amplifier having an input circuit and an output circuit, unidirectional electric current devices coupled to said input and output circuits, means coupling the outputs of said unidirectional devices to said amplifier to maintain constant the ratio of output to cascaded electron discharge devices each having an input circuit and an output circuit and an anode, a cathode and a grid, the output circuit of the first of said devices being coupled to the inputv circuit of the second device, a source of potential and a resistor serially connected between the grid and cathode of the first device, a connection including a source of potential from the grid of the second device to the end of said resistor connected to the cathode of the first device, and a connection from the cathode of the second device to the end of said resistor to which the grid of the first mentioned device is connected whereby grid current flow of the second device varies the potential on the grid of said first device in such a way as to introduce into said second device potentials to compensate for the distortion caused by the grid current flow in said second device.

29. An amplifying system comprising a first pair of electron discharge devices each having an anode, a cathode and a grid, a second pair of electron discharge devices each having an anode, a cathode and a grid, input and output circuits connected to the input and output electrodes of said pairs of devices, the output circuit of said first pair of devices feeding the input circuit of said second pair of devices, a resistor connected between the cathodes and grids of said second pair of devices, and a connection from the end of said resistor to which the cathodes of said second pair of devices are connected and the grids of said first mentioned pair of devices whereby grid current fiow in said second pair of devices causes a variation in potential across said resistor which variation in potential alters the grid bias on said first mentioned pair of devices in such a way as to introduce compensating potentials into said second pair of devices as to reduce distortion caused by the grid current flow in said second pair of devices.

CLARENCE W. HANSELL. 

